1. Field of the Invention
The invention relates to a vibration reducing technique for an impact tool which linearly drives a tool bit by means of a swinging member.
2. Description of the Related Art
Japanese non-examined laid-open Patent Publication No. 2008-73836 discloses an electric hammer drill that drives a hammer bit by using a swinging mechanism (also referred to as “swash mechanism”). The kwon art includes a vibration reducing mechanism having a dynamic vibration reducer mounted to a tool body of the hammer drill. The dynamic vibration reducer is designed to actively drive or forcibly vibrate a weight of the dynamic vibration reducer by directly utilizing swinging movement of a swinging member in the form of the swinging ring and thereby reduce vibration caused during hammering operation. Thus, regardless of magnitude of vibration that acts upon the impact tool, the dynamic vibration reducer can be steadily operated.
The known vibration reducing mechanism is of the mechanical type that vibrates the dynamic vibration reducer by using machine parts directly operated by swinging movement of the swinging ring. Therefore, the number of machine parts relating to such vibration increase and it is necessary to move the weight of the dynamic vibration reducer in a direction opposite to the direction of movement of the hammer bit. Due to these facts, a vibration mechanism section has to be disposed on the opposite side of the center of swinging movement from a hammer bit driving mechanism section and is thus difficult to dispose by utilizing a free space within the tool body. Therefore, in these respects, further improvement is required.